基于Lagrange方法封闭的两相湍流场方程模型

两相湍流场方程模型采用基于Euler方法的一阶矩方程,而二阶矩方程由Lagrange方法得到,新模型的封闭不需要附加其它假设.首先基于概率密度函数给出颗粒运动的连续方程和动量方程,其次由基于平均Langevin方程的Lagrange模型推导得到颗粒二阶矩方程,最终获得封闭的二阶矩模型.将新模型用于气固两相壁面射流的数值模拟,结果表明新模型合理有效.     

基于小关联时间两相湍流色噪声的近似模型及数值模拟

从一般高斯型色噪声模型出发,通过泛函导数,应用小关联时间,近似计算多维色噪声,得到有效Fokker-Planck方程.将其应用到两相湍流中得到颗粒相的概率密度函数输运方程,从而得到颗粒相的二阶矩模型.将颗粒应力方程简化成代数方程,建立代数应力模型.将对流扩散方程的有限分析法运用到求解两相流模型中,对壁面两相射流进行数值模拟,并将求解结果与实验结果进行对比分析.     

两相湍流统一色噪声法概率密度函数模型

统一色噪声近似方法对简单一维色噪声问题研究较为充分, 本文将统一色噪声法应用到高度复杂的多维气固两相湍流系统之中.首先从颗粒运动Langevin方程出发, 利用统一色噪声法获得两相湍流Fokker-Planck方程, 然后以此为基础建立颗粒轨道两阶矩模型.文中建立的新模型成功应用于后台阶两相湍流流场的数值模拟, 预报合理正确.研究表明, 对于多维两相湍流系统, 统一色噪声法仍然行之有效.     

快速流化床内相分布现象的初步动力学分析

借助于双流体模型建立了快速流化床内充分发展状态颗粒相与气相平均湍流运动方程组.两相联合径向动量方程的形式揭示了床内径向空隙率分布对于当地湍流结构的依赖关系,并解释了两相流中相分布现象存在的一般性.两相联合动量方程的数值求解示范结果表明床内空隙率分布的变化趋势与实验基本吻合,为模型的合理性提供了一种佐证.     

基于拉氏概率密度的两相湍流二阶矩模型

用颗粒运动的拉氏分析和PDF方法,改进了颗粒相的二阶矩模型。由拉氏两相运动的随机微分方程出发,采用随机过程分析和信号分析法得到湍流两相流动的PDF输运方程,双流体模型方程和两相脉动速度相关的基本模式的封闭式,和用其它方法导出的方程与封闭式的结果一致,对封闭式作了重要的改进,在分析颗粒轨道上的流体湍流作用时间时,全面地引入拉氏分析的轨道穿越效应、惯性效应、连续效应和湍流的各向异性。     

湍流两相流动有燃烧颗粒相概率密度函数输运方程理论

由有燃烧的湍流气粒两相流动的瞬态方程和统计力学概率密度函数概念出发,推导了有燃烧颗粒相的质量－动量－能量联合概率密度函数（ＰＤＦ）输运方程,并对方程中条件期望项用梯度模拟概念进行了模拟封闭。封闭后的ＰＤＦ方程可作为建立颗粒拟流体模型方程和封闭二阶矩模型的基础,也可以通过Ｍｏｎｔｅ－Ｃａｒｌｏ 法求解用以直接计算颗粒雷诺应力和湍流动能,以便和二阶 矩模型的结果相对照,改善二阶矩模型。     

下降管中稠密两相湍流的数值模拟

本文将统一二阶矩两相湍流模型和颗粒动力学理论结合,推导并封闭了稠密两相流考虑颗粒间碰撞的统一二阶矩两相湍流模型。该模型用颗粒动力学理论模拟颗粒之间的碰撞,用各向异性的统一二阶矩模型考虑气相和颗粒相的湍流脉动,并用输运方程描述气固两相湍流之间的相互作用。最后用该模型对下降管中的气粒两相流动进行了模拟,模拟所得的沿径向颗粒浓度分布和速度分布与实验吻合较好,预报结果也反应出了颗粒雷诺应力的各向异性。     

颗粒增强湍流的新模型和气粒流动的湍流变动

用雷诺应力方程模型和极细的网格系对单个颗粒受湍流气体绕流进行了数值模拟,研究了改变颗粒直径和气体相对速度时颗粒增强气体湍流的规律.据此构造了颗粒尾涡增强气体湍流的新模型.将此子模型加入到两相流动模型中,对竖直和水平通道内气粒两相流动进行了数值模拟,和实验结果的对照表明,考虑颗粒尾涡增强气体湍流效应得到的气体湍流脉动速度的模拟结果比不考虑此效应的模拟结果好得多.     

k－ε－PDF两相湍流模型和台阶后方气粒两相流动的模拟

本文提出了两相湍流的ｋ－ε－ＰＤＦ模型。ＰＤＦ模型所得的湍流两相流动的统计平均方程，与雷诺时均方程有相似的形式，但ＰＤＦ模型可精确计算出颗粒相各方程的脉动关联项。本文将该模型用于预报台阶后方湍流两相流动，与ｋ－ε－ｋｐ模型相比，它可以更合理地预报出颗粒湍流的各向异性。     

DSM-LPDF两相湍流模型及旋流两相流动的模拟

本文由流体－颗粒速度的拉氏联合概率密度函数（ＰＤＦ）输运方程出发,用Ｓｉｍｏｎｉｎ建议的Ｌａｎｇｅｖｉｎ模型封闭颗粒所遇到流体瞬时速度的条件期望项,并用Ｍｏｎｔｅ Ｃａｒｌｏ方法直接求解 ＰＤＦ输运方程,将其和求解流体雷诺应力方程模型的有限差分方法结合,建立了雷诺应力－拉氏ＰＤＦ（ＤＳＭ－ＬＰＤＦ,简称ＤＬ）两相湍流模型．用此模型模拟了旋流数为０．４７的突扩旋流气粒两相流动,并与文献中ＰＤＰＡ实验和用类似于单相流动湍流模型封闭方法的时平均统一二阶矩（ＵＳＭ）模型的预报进行了对比．     

A momentum exchange-based immersed boundary-lattice Boltzmann method for simulating incompressible viscous flows

A momentum exchange-based immersed boundary-lattice Boltzmann method is presented in this Letter for simulating incompressible viscous flows. This method combines the good features of the lattice Boltzmann method (LBM) and the immersed boundary method (IBM) by using two unrelated computational meshes, an Eulerian mesh for the flow domain and a Lagrangian mesh for the solid boundaries in the flow. In this method, the non-slip boundary condition is enforced by introducing a forcing term into the lattice Boltzmann equation (LBE). Unlike the conventional IBM using the penalty method with a user-defined parameter or the direct forcing scheme based on the Navier–Stokes (NS) equations, the forcing term is simply calculated by the momentum exchange of the boundary particle density distribution functions, which are interpolated by the Lagrangian polynomials from the underlying Eulerian mesh. Numerical examples show that the present method can provide very accurate numerical results.     

喷动流化床的数值模拟研究

本文借鉴 Ｃｕｎｄａｌｌ＆ Ｓｔｒａｃｋ提出的碰撞模型,将欧拉方法和拉格朗日法结合起来,建立了喷动流化床气固两相流动的数学模型,在计算机上对试验台进行了模拟,探讨了床内颗粒的运动特征。按１：１的比例建立了喷动流化床的模型试验台并进行了试验,对模拟结果和试验结果进行了比较与分析。颗粒在喷动床内的运动特征,模拟结果都能够再现出来,模拟结果与试验结果取得了很好的一致性。     

空间发展湍流气粒两相平面混合层的大涡模拟与统计

本文对空间发展的湍流气固两相平面混合层流动进行了大涡模拟研究,其中气相亚网格尺度（SGS）使用结构函数模型,气相控制方程组采用SIMPLE方法求解,固体颗粒运动用拉格朗日方法计算。计算结果正确重现了流体涡结构的卷起、合并和破碎过程,以及小尺寸颗粒在涡边缘（低涡度区）的局部富集现象。对直径分别为42μm、72μm和135μm分别进行了模拟,并将统计结果和实验测量结果（Hishida　et　al[1]）比较,表明两者的平均速度吻合很好,但颗粒数密度和脉动速度存在较明显的差异,因此有必要对亚网格应力和颗粒之间的耦合作用以及拟序结构的三维性对颗粒运动的影响开展深入研究。     

A direct-forcing fictitious domain method for particulate flows

A direct-forcing fictitious domain (DF/FD) method for the simulation of particulate flows is reported. The new method is a non-Lagrange-multiplier version of our previous DLM/FD code and is obtained by employing a discrete δ-function in the form of bi(tri-) function to transfer explicitly quantities between the Eulerian and Lagrangian nodes, as in the immersed boundary method. Due to the use of the collocation-point approach for the rigidity constraint and the integration over the particle domain, the Lagrangian nodes are retracted a little from the particle boundary. Our method in case of a prescribed velocity on the boundary is verified via the comparison to the benchmark results on the flow over a fixed cylinder in a wide channel and to our spectral-element results for a channel with the width of four cylinder diameters. We then verify our new method for the case of the particulate flows through various typical flow situations, including the sedimentation of a circular particle in a vertical channel, the sedimentation of a sphere in a vertical pipe, the inertial migration of a sphere in a circular Poiseuille flow, the behavior of a neutrally-buoyant sphere in Couette flow, and the rotation of a prolate spheroid in Couette flow. The accuracy and robustness of the new method are fully demonstrated, in particular for the case of relatively low Reynolds numbers and the neutrally-buoyant case.     

介观尺度通道内多相流动的耗散粒子动力学模拟

采用四次方光滑函数构造了包含远程吸引近距排斥的保守力势函数, 应用该势函数, 采用耗散粒子动力学方法, 对十字型微通道内的多相流动进行了计算. 计算结果表明, 该势函数能有效模拟十字型微通道内的流动过程及模式. 关键词： 多相流 耗散粒子动力学 保守力势函数     

通道中串列旋转圆柱的格子Boltzmann-虚拟区域方法的模拟

通过结合格子Boltzmann方法(LBM)和虚拟区域(Fictitiou sDomain)思想,建立格子Boltzmann-虚拟区域(LB-DF/FD)方法.采用两套网格系统,欧拉网格用于流体,拉格朗日网格用于固体.原有的LBM在计算运动固体的受力方面存在数据振荡,LB-DF/FD方法改进了此缺陷.为验证该方法,模拟圆柱绕流、圆形颗粒在无限长通道中平动及在无限大流场中转动三种情况,结果与其他数值解及理论解符合得很好.利用该方法模拟低雷诺数下通道中串列旋转圆柱周围的流场,分析圆柱间距(g)及雷诺数(Re)对流场结构的影响.给出Re=0.001,0.1和10下,0.2≤g≤8.0的流线结构、圆柱升力、阻力以及力矩等数值结果.结果表明,g对流场的结构及圆柱的受力有显著影响,Re对圆柱阻力及Stokes单元数目的影响较大.     

On the Mixed Propagator Approach to ρ-ω Mixing

The mixed propagator (MP) approach to ρ-ω mixing is discussed. It is found that under the pole-approximation assumption the results of MP approach is not compatible both with the effective Lagrangian theory and with the experiment measurement criterion. To overcome these inconsistent, we propose a new MP approach in which the physical states of ρ and ω are determined by the requirement of experimental measurement to meson resonance. In terms of this new MP approach, the EM pion form factor F_π and form factors of ρ⁰→π⁰γ and of ω→π⁰γ are derived. The results of F_π are in good agreement with data. The form factor of ρ⁰→π⁰γ exhibits a hidden charge-asymmetry enhancement effect which agrees with the prediction of the effective Lagrangian theory.     

基于界面捕捉的三维多介质辐射流体力学方程MMALE计算方法

针对界面重构产生的混合介质网格,建立基于能量守恒的子网格封闭模型,给出基于混合介质网格上的三维扩散方程求解方法.在此基础上,结合界面重构和流体力学方程MMALE （multi-material arbitrary Lagrangian-Eulerian）算法,给出一种针对三维辐射流体力学的MMALE计算方法.采用解析解算例,验证算法的正确性和精度.通过对典型辐射驱动问题的模拟,展示方法的健壮性.     

Dispersion simulation of a wind tunnel experiment with Lagrangian particle models

Summary A particle model LAMDA suitable for dealing with the atmospheric dispersion is presented. The reliability of the model is tested comparing the results of its simulations to the wind tunnel measurements by Khurshudyanet al. (1981). Two versions of the model, both based on the Langevin equation and askewed distribution of the vertical wind velocity fluctuations, are considered. To develop the second version of the model we derived a proper scheme to produce skewed distributions of particle velocities consistent with the observed first and second moments of turbulent fluctuating velocities, with their horizontal and vertical derivatives, and their cross-correlations. The 2D geometry of the obstacle (in the wind tunnel experiment considered) allowed some simplifications. Due to the lack of some input data (such as the vertical profiles of crosswind standard deviation of wind velocity fluctuations and of the Lagrangian time scales) we looked for three different parametrizations. It was found that particular combinations of measured and parametrized data could give rise to critical vertical regions in which the derived scheme for the generation of random vertical velocity fluctuations cannot be applied. The best vertical distributions of the Lagrangian time scales (third parametrization) were estimated by fitting simple formulations for the average plume height and lateral variances to the measured data. The main results of this work were the model performance in simulating dispersion in shear flow over flat terrain, and its sensivity to the shape of the crosscorrelation term .